Multichannel Expansion with PV_BrickWall

Hi -
I wanted to test four channels into the PV_BrickWall filter. I’m not able to explain the results. I seem to only be getting two channels of output, with most of the signal on the first channel.
Can anyone help me understand this? Thanks.

    var in, chain;
    in =!4;
    chain = FFT(LocalBuf(2048, 4), in);
    chain = PV_BrickWall(chain,;
FFT(Array.fill(4, { LocalBuf(2048, 1) }, in)

FFT buffers must be single-channel only, but you can use one buffer per channel.